1. Technical Field
This invention relates to a test structure pattern and a method of processing the electrical data extracted from it enabling the measurement of the width of thin-film conductors formed on substrates down to approximately 5 microns in length with precision of the order of one nanometer.
2 DESCRIPTION OF THE PRIOR ART
The prior art is limited to structures which obtain measurements requiring a very long line to eliminate measurement uncertainties. However, these long lines also provide the undesired side effect of averaging out any local non-uniformities in the line being measured.
A typical method for determining the width of a thin film conductor is by use of the cross-bridge resistor (see Ref. 1) (FIG. 1), where the linewidth is W.sub.0 determined by: ##EQU1## where R.sub.b is the resistance of the bridge (that is, of the thin-film conductor 20 between pads 5 and 6), R.sub.S is the sheet resistance of the conducting material, as measured using the van der, Pauw cross portion of the test structure extending between pads 2, 3, 4 and 5, and L.sub.b is the length of the bridge. However, Eq. (1) presumes an ideal, uniform the linewidth W.sub.bt corrected for current shunting at finite width voltage taps such as extending between pad 5 and line 20 is given by ##EQU2## where the correction E is given by [2] ##EQU3##
That is, the correction E provides compensation for lower resistance and increased electron flow past the taps, such that W.sub.bt correctly reflects the width of the bridge.
However, it has long been realized that a useful result for the correction can be obtained using equations (2) and (3) only where D, W.sub.b, and W.sub.S are known and are fabricated with exact 90.degree. corners, (i.e., in no real or practical case). Historically, equation (3) has been used to create guideline design rules that minimize E so W.sub.bt is approximately equal to W.sub.b. This is done by designing the test structure such that W.sub.b .apprxeq.D and L.sub.b &gt;&gt;W.sub.b. Typical design rules require that for a bridge with W.sub.b =1 .mu.m, L .gtoreq.80 .mu.m. The requirement of such long lines precludes detection of local variations in the linewidth. Therefore the prior art test structure and method are incapable of accurate characterization of short conductors, as are commonly employed.
Those concerned with these and other problems recognize the need for a test structure pattern and a method of processing the electrical data extracted from it that enables the measurement of the width of a short line with precision.